Simulation of bubbly flow in loop reactors using the Eulerian-Eulerian two-fluid method: Analysis and assessment of medium-to-high liquid flow rate effect

Loop reactors in the chemical industry are characterised by gas–liquid flow in a vertical arrangement, including a riser and a downcomer, at relatively high liquid velocities. A standard method in the industry for simulating such flows in large geometries is the Eulerian two-fluid model, which relies on interfacial forces to describe the interactions (momentum transfer) between the two phases. However, most of these models have been validated with data from bubble columns and low-velocity pipe flows. Therefore, we assess the accuracy of these models against experimental data from medium-to-high velocity (upward and downward) bubbly flows in pipes. The OpenFOAM simulation framework is used for this purpose. For upward flows, current models fail to predict the shift of the void fraction peak towards the centre of the pipe at high liquid velocities. This work discusses several development directions, including adjustments to the lift and wall lubrication coefficients, which significantly improve prediction accuracy. For downward flows, the void fraction distribution is highly dependent on inlet conditions, which aligns with previous results from the literature. This study highlights the mispredictions of conventional models and provides valuable insights into optimising interfacial force models for more accurate simulations in chemical loop reactors.